Which of the following is a subcategory of navigation rules?

The selection of a subcategory of navigation rules refers to the classifications that help mariners understand how to navigate safely on the waterways. The option stating "In any vis, conducted in sight of each other" pertains to the navigation rules specifically designed for situations where vessels can see one another. These rules provide guidelines for preventing collisions by establishing protocols based on visibility conditions, which are critical for safe navigation.

When vessels are in sight of each other, the navigation rules focus on maintaining safe distances, signaling intentions, and maneuvering according to the actions of other vessels. This is essential for ensuring safe passage and reducing the risk of accidents when visibility allows for direct observation between vessels.

Other options do not accurately represent established subcategories of navigation rules. Navigation rules are not limited to written guidelines alone or restricted to nighttime scenarios, and they do not require specific permission from the Coast Guard for adherence. Each of these elements plays a role in broader navigation regulations, but only the visibility-based conduct directly addresses interaction between vessels. Therefore, the rules applied when vessels are in sight of one another form a crucial part of navigation safety protocols.